Fix hidden code navigation tabs

What does this MR do and why?

Follow-up from !153244 (comment 1909342620)

A couple months ago we introduced Tailwind CSS. As we were migrating gl-display-none to gl-hidden we noticed that /app/assets/javascripts/code_navigation/components/popover.vue#L93 was using gl-hidden but prior to Tailwind CSS it wasn't doing anything. Now that we have Tailwind CSS it was hiding the tabs. This MR removes the gl-hidden class to fix the bug.

Screenshots or screen recordings

Before	After

How to set up and validate locally

This setup requires having a runner configured - https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/runner.md?ref_type=heads

1. Find a project with JavaScript files
2. Create a .gitlab-ci.yml file with the following:

code_navigation:
  image: sourcegraph/lsif-node:v0
  allow_failure: true # recommended
  script:
    - lsif-tsc **/*.js --AllowJs --checkJs
  artifacts:
    reports:
      lsif: dump.lsif

3. Go to a JavaScript file and click on a definition